Under the advancement of microelectronics technology and software technology, both wireless (e.g. cellular) communication networks and wire communication networks have been developing towards digitalization, personalization, wide-band, intelligent and multi-media. The wide-band digitalization has become the foundation in a base station system of a cellular communication network. Digital devices of an intermediate frequency portion, even a radio frequency portion, have been used to substitute analog devices. A concept of wide-band multi-carrier base station has appeared. Comparing with a narrow-band base station, a wide-band multi-carrier base station has outstanding features of generality and flexibility. For example, different band width, different system and different application required by users can be satisfied by changing software settings of a digital portion.
A gain of respective carriers of shared portions in a transmitting channel of a wide-band multi-carrier base station has a certain inconsistency. Common portions of the respective carriers of a transmitting channel of the wide-band multi-carrier base station comprise a wide-band high rate digital to analog converter (DAC), a wide-band transmitter, a wide-band linear amplifier, and an antenna feeder. The antenna feeder typically has ideal amplitude-frequency characteristics within a very wide frequency band. Therefore, the difference of the respective carriers caused by the antenna feeder is normally not considered. An output of the DAC has an amplitude-frequency characteristic according to a scrolling down Sinc function, and an output signal amplitude response at Fs/2 (Fs is clock frequency) is 3.92 dB lower than that of at 0 frequency. This is an extreme condition that is actually not used. However, if the bandwidth of a wide-band multi-carrier is larger than Fs/10, the gain difference between the respective carriers caused by the DAC will reach 0.5 dB, even 1 dB. The gain difference between the respective carriers in an operation frequency band of the wide-band transmitter and wide-band linear power amplifier can also reach 1 dB, even 2 dB. In this way, after a plurality of digital intermediate frequency signals with the same amplitude passing through the wide-band transmitter, the final output power difference of the respective carriers is possible to reach 0.5 dB, even above 2 dB.
When designing a system, it is required that each of the carriers exceed a design nominal value. For a wide-band multi-carrier system, it is required that the maximum power outputted by a carrier with the lowest gain reach the nominal value. In this way, the maximum transmitting power of the other carriers in the system can exceed the nominal value or even can reach a value above 2 dB. Thus, a larger power tolerance is reserved for the common portions of the respective carriers of a transmitting channel, particularly the power amplifier. Accordingly, this causes the difficulty of designing a system and the increasing of the cost.